noun
dōjinshi; fanzine; self-published magazine
A magazine or book created by a group of like-minded people, often for a niche audience. In English contexts, 'dōjinshi' is widely understood among fans of Japanese pop culture.
コミケで新しい同人誌を買った。
I bought a new dōjinshi at Comiket.
彼はSF小説の同人誌を発行している。
He publishes a dōjinshi of science fiction stories.
商業誌 is a commercial magazine, in contrast to the self-published nature of 同人誌.
From 同人 (dōjin, 'like-minded people') + 誌 (shi, 'magazine').